Storage tanks are used throughout the world for storing various liquids in bulk form. In particular, storage tanks are used extensively for the storage of liquid gasoline at retail gasoline stations. Necessarily, these stations are in populated areas and therefore there is always a danger associated with leaks from the tanks. Leaked gasoline poses a hazard to the environment as well as an obvious health hazard. The known problem is particularily troublesome in that gasoline storage tanks are usually buried underground and any leaks which develop are normally very slow initially. This means that any leak which does start is difficult to detect until a substantial amount of gasoline has leaked. By that time environmental damage and possible health problems have occurred. The time and expense needed to clean up a gasoline spill can be enormous. It could involve initially emptying the storage tank and removing the emptied tank from the ground. The ground surrounding the tank would have to be decontaminated, a procedure which could be extensive in case of a slow leak which is not detected early or a sudden large leak. In addition to the expense of the above clean-up, there is the loss of profits due to the down-time involved not only with the damaged tank but also possibly the whole gasoline station. The health hazards associated with a gasoline spill can also be enormous in case of an accidental fire or drinking water contamination.
Use of conventional underground storage tanks is particularly troublesome in those areas that are prone to earthquakes. Typical underground storage tanks are constructed of metal or fiberglass. Any earthquake is likely to cause a crack in the tank with a consequent leak. If the leak is slow, the same problems as above discussed exists. If the leak is fast, the problem is readily detected, but only after it is too late to do anything about.
The problems associated with the present underground storage tanks are well known. Various attempts have been made to aleviate the problems. Several different types of leak detectors are presently being marketed in order to detect even slow leaks. A reliable leak detector would be of some value in that a leak which is detected early enough can be corrected. This may involve the emptying of the tank under controlled conditions and the repair of the tank. Such an operation would be expensive, however it would solve the problem. Another attempt to correct one of the problems has been the use of vault systems. That is, the rigid storage tank is surrounded by another rigid tank or shell which acts as an containment vessel if the storage tank developes a leak. This, of course, is quite expensive and economically lends itself only to tank systems which are being installed. It would be prohibitively expensive to uncover an existing storage tank and fit it with a rigid outer shell. Also, a problem still exists with any vault system in those areas that are prone to earthquakes. If the earthquake is severe enough, it would not only crack the storage tank but also the outer containment vessel.
There has now been discovered a liquid storage tank system which solves many of the problems inherent with the existing systems. The system of this invention is economical in that it can be installed in an existing underground storage tank as well as in new storage tanks about to be installed. The new system also eliminates the problem associated with the vaulted systems in that the new system is earthquake-proof.